Maximum Matchings in Geometric Intersection Graphs.

Let G be an intersection graph of n geometric objects in the plane. We show that a maximum matching in G can be found in O ( ρ 3 ω / 2 n ω / 2 ) time with high probability, where ρ is the density of the geometric objects and ω > 2 is a constant such that n × n matrices can be multiplied in O ( n ω ) time. The same result holds for any subgraph of  G , as long as a geometric representation is at hand. For this, we combine algebraic methods, namely computing the rank of a matrix via Gaussian elimination, with the fact that geometric intersection graphs have small separators. We also show that in many interesting cases, the maximum matching problem in a general geometric intersection graph can be reduced to the case of bounded density. In particular, a maximum matching in the intersection graph of any family of translates of a convex object in the plane can be found in O ( n ω / 2 ) time with high probability, and a maximum matching in the intersection graph of a family of planar disks with radii in [ 1 , Ψ ] can be found in O ( Ψ 6 log 11 n + Ψ 12 ω n ω / 2 ) time with high probability.